Real Fiero Tech

Has anyone cc'ed the 3.4 dohc?

Im working designing a set of pistons for mine but i need to know the cc's so I can figure how much I need to move the pin height to lower the comp. ratio.

I want to drop it to around 8.5 so my turbo will be happy :thumbleft:

Im planning on using scat 6" sbc rod with the small journal and a .010 under bearing, cryo ed crank w/ shot peening, oil squrters and LOTS of boost!!

oil squirters how?

If you're going to use 6" rods and the 84 mm crank, you're going to have about as much compression height as a 400 Chevy with 6" rods... almost none. 1.156" or so. There's VERY little room for a dish with compression height that shallow.

ok the stock rod is 5.960" so .040 isnt gonna make "very little" comp. it would bring up the comp. as it would raise the stock piston .040. not much but it would.

Thats why I desginging a piston. But i ill need to know the cc's So I can figure out where the pin hole has to go.

oil Squrtirs, Im still not exactly sure the best way to go about it or all the details but planning to tap into an oil passege on the insde of the block and running like a 1/8 line to the center of the "v" ( underneath the balance shft)and then seperate them in to seperate squrtires to cool the pistions.

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The heads are around 52 cc's and the pistons are around 5 cc's

If you use iron head pistons for a 3.4 then that will give you a rough compression ratio of 8.5:1

Stock rods in a 3.4 are 5.7 inches NOT 5.9

OK, thanks for the info,

I guess either i miss heard or the guy I was talkin to at gm dosent know what he was talking about.... my bad.

The new 3500 motors have 5.9 inch rods. But not the dohc engines.

mrsleeve91 wrote:( underneath the balance shft)

If you think that's a balance shaft and that the stock rods are 5.960, then you really need to reevaluate your build plan.

Going to 6" rods with the 84mm stroke will put the piston pin so close to the piston crown that you won't have room for a dish. You DO know what compression height is, right?

ok ok "intermediate shaft"......
the rods, thats what I was told.
Im learning as I go here

So you can go fuck yourself!

.

Gentlemen, settle down.

mrsleeve91 wrote:ok ok "intermediate shaft"......
the rods, thats what I was told.
Im learning as I go here

If you don't use the correct terminology, we'll have to GUESS at what you're talking about, and probably guess whether or not you even know what you're talking about. If I have to guess that, my guess is going to be "no". So pay attention to what you type or you'll always going to be getting crossed up with people.

You WILL have to reevaluate your build plan. If you use 6" rods, you're not raising the pin by .040 as you thought, you're raising it by .300. That's a big difference and, as I said, will most likely leave you with insufficient compression height for much, if any, dish.

Even if the stock rod were 5.960, there is NOT room to raise the piston by .040 without hitting the cylinder head at high RPM.

The intermediate shaft has ZERO eccentric weight and is far too light to be a balance shaft. I'm not sure, but I think that balance shafts also typically turn at twice crank speed. The intermediate shaft turns at half crank speed.

Shaun41178(2) wrote: If you use iron head pistons for a 3.4 then that will give you a rough compression ratio of 8.5:1

Shhhhhhh...... Thats the Holy Grail....... :thumbleft:

BTW

The intermediate shaft is just a freaking dumb solution to turn the oil pump. :cussing:

Be fun to remove it... If there was a better way to make it turn the cams, too :scratch:

Remote oil pump ftw? All that preoilling goodness...

You could get rid of it if you're running dry sump and can figure out how to still turn the timing belt.

Shaun41178(2) wrote: If you use iron head pistons for a 3.4 then that will give you a rough compression ratio of 8.5:1

I still don't think you can do that because the compression heights are the same and the 3.4 OHV pistons don't have the valve reliefs cut into the edges of the crown.

Ok that was my fault on the bad info and incorrect termonology, Ive built a few engines but they were basicly stock rebuilds.
Im just try to roughly figure out what I need to do to drop the comp. and "beef up" the bottom end.
As for reevaluation, ok I just have to use a 5.7 rod. still a lagre avalb. although clearencing is a posible issue that conceerning me.

let me get this straight. On a dohc, the crank turns the intermediary shaft via the regular 60* tiing chain setup. then that shaft turns the cams via a belt? I need a pic of a dohc front. This could throw off my dohc 2.8 block plans.

The dohc uses an internal cam with no lobes that sticks out the far end of the block and turns the pulleys.

3.4dohc has 5 cams, 1 timing chain and 1 timing belt.

p8ntman442 wrote:let me get this straight. On a dohc, the crank turns the intermediary shaft via the regular 60* tiing chain setup. then that shaft turns the cams via a belt? I need a pic of a dohc front. This could throw off my dohc 2.8 block plans.

Retarded, ain't it? I can't imagine who designed that thing for GM, but its a little surprising how good the engine is considering some of the idiotic things they did when they designed it.

Fastback86 wrote: Retarded, ain't it? I can't imagine who designed that thing for GM, but its a little surprising how good the engine is considering some of the idiotic things they did when they designed it.

Second that!!


My conclusion is that the retard who designed this engine had a pushrod mentality. :scratch: